The cornea depends on a high degree of cellular differentiation to fulfill its unique functions as an optically clear barrier and refractive surface at the front of the eye. The deceptively simple overall structure of corneal epithelium, stroma, and endothelium is ultimately dictated by the spatial and temporal regulation of gene expression in these cells. Because the molecular events that control phenotypic expression in the layers of the cornea are very poorly understood, we have undertaken to isolate and characterize genes that are preferentially (and perhaps uniquely) expressed in the corneal epithelium and endothelium, using a range of molecular biological techniques. Peptide microsequencing of corneal protein samples from human, mouse, kangaroo, chicken, and squid has shown that many of the major soluble proteins in the cornea are enzymes, recruited in evolution for a structural, rather than catalytic, role. These findings extend the theory of gene sharing, proposed in this laboratory to explain observations made in the lens, to another transparent ocular tissue, the cornea. We have identified one particular corneal peptide; its sequence, which is identical in mouse and man, has never been described. We are now actively trying to characterize this 60 kD protein and its gene. Class 3 aldehyde dehydrogenase (ALDH Cl3) is expressed at very high levels in the corneal epithelium of mammals, thus we have isolated the promoter region for this gene and plan to use it to direct expression of other genes to the cornea. Such a promoter/structural gene construct may have ultimate use in directing topical gene therapy to this exposed part of the eye.